1. Field of the Invention
The present invention relates to a wavefront sensor, and more particularly, to a sensor that measures a wavefront of a lightwave by using shearing interferometry.
2. Description of the Related Art
Interferometers using an interference phenomenon of the lightwave have been widely used for high-precision measurements because noncontact measurement is enabled with a precision that is equal to or better than the wavelength of light.
For example, JP 07-77413 A discloses a shearing interferometer that splits an optical wavefront to be measured into two optical paths, displaces the positions of those wavefronts from each other, mixes those wavefronts together again to measure the configuration of the optical wavefront to be measured based on the interference fringe of the mixed optical wavefront.
However, it is known that, when the wavefronts that have been split into the two optical paths are mixed together again to observe the interference fringe (intensity after interference) on the interference measurement plane, the propagation optical path difference between those two optical paths up to the interference measurement plane varies depending on the arrival direction of the optical wavefront to be measured. Accordingly, different interference states are formed for different directions along which the optical wavefronts to be measured arrive. As a result, lights having different interference states are combined together on the interference measurement plane for wavefronts from a light source that cannot be regarded as one point, or for wavefronts from a point light source that moves beyond a distance that can be regarded as one point due to the vibrations of a device or the like. This causes such a problem that the wavefront configuration cannot be measured by observing the interference fringe.
The present invention has been made to eliminate the above problem, and therefore an object of the present invention is to provide a wavefront sensor which is capable of measuring wavefronts from light sources which cannot be regarded as one point such as surface light sources, a plurality of point light sources, or wavefronts from point light sources that move beyond a distance that can be regarded as one point.